By MICHAEL WILSON and COLIN MOYNIHAN

Published: September 6, 2004

The former boyfriend of a woman who was dating another man burst into a home in the Gravesend section of Brooklyn yesterday and shot and killed the man and the man's 73-year-old father, the police said. He then fled to a nearby schoolyard and turned the rifle on himself, the authorities said.

The violence began at 10:40 a.m., the police said, when the ex-boyfriend, Michael Jobsky, 42, of 440 Neptune Avenue, in Coney Island, entered the victims' two-story red-brick home at 1917 West 13th Street. Mr. Jobsky was enraged because Vincent Rotundo Jr., 40, was seeing a woman whom Mr. Jobsky had broken up with about two years ago, according to neighbors.

The girlfriend, who was at the home, was not identified by the police.

Mr. Jobsky went to the basement and shot Mr. Rotundo and threatened to slit the throat of the girlfriend, who managed to escape, screaming, into the street, neighbors said.

Mr. Rotundo's parents, Vincent Sr. and Gloria, ran to the basement to help their son, hitting Mr. Jobsky with a broom, neighbors said. At one point, the gunman may have barricaded himself in a bathroom.

Mr. Jobsky shot the elder Mr. Rotundo in the face and fled the house, the police said. He ran several hundred feet to a yard at Public School 97, where he killed himself, the police said. A rifle could be seen beside his body yesterday afternoon as investigators questioned neighbors and passers-by.

''Stupid, stupid,'' one woman said. ''That's terrible.''

Several witnesses said that a few hours earlier, at 4 or 5 a.m., there had been a fight in which Mr. Jobsky had vandalized the younger Mr. Rotundo's pickup truck. The witnesses said the police were called, but it was unclear whether Mr. Jobsky was there when they arrived.

''The man was on a rampage,'' said Donna Padilla, 41, a neighbor.

Law enforcement authorities, however, said last night that they had no knowledge of an earlier fight.

Single-family homes and row houses line the blocks around the crime scene, many with Italian flags flying from the front porches.

The Rotundos were a close-knit family, and it was not unusual for them to drop by unannounced with fresh red sauce for pasta, neighbors said.

The neighbors described how Gloria Rotundo began sobbing, ''My Vinny! My Vinny!'' and would not leave the scene yesterday when she realized that her husband was dead. A window pane of their home was shattered during the attack.

The Rotundos' daughter, Danna Biancaniello, who lives next door, was taken to a hospital in shock after she heard the news and collapsed with grief in the street, witnesses said. ''How can I go on without my father and my brother?'' she said to a friend, Deborah Verstandig, in the back of an ambulance on the way to the hospital , Ms. Verstandig said.

The younger Mr. Rotundo and his father worked together in a fuel oil business, filling people's furnaces. The elder Mr. Rotundo also worked as a tile layer and in a toy factory, neighbors said.

He spent almost every morning fishing at Gravesend Bay, stopping first for coffee and a newspaper.

Photos: Medical workers and police officers escorted relatives from the scene of a shooting in Gravesend, Brooklyn.; A detective examines the body of a man who the police said killed two men in a jealous rage. The man shot himself at a nearby schoolyard. (Photographs by Edwine Seymour for The New York Times)